FIG. 1 illustrates a conventional drilling gun 100 configured to be inserted into a shaft in which drilling is to occur. The drilling gun 100 includes a chamber 102 into which a cartridge 104 from a magazine 106 is inserted. The cartridge 104 includes a center projectile 108 surrounded by six peripheral projectiles 110. All of the projectiles 108, 110 are parallel to each other when inserted into the chamber. The center projectile 108 fits into a center barrel 112 of the gun 100. The peripheral projectiles 110 respectively fit into the peripheral barrels 114 of the gun 100. The peripheral barrels 114 are curved so as to cause the initially-parallel peripheral projectiles 110 to diverge upon firing of the cartridge 104. The pattern of diverging projectiles caused by the organization and shape of the barrels 112, 114 facilitates drilling.
It is preferable that the cartridge 104 be made of a combustible material that leaves no structural components in the chamber 102 upon firing of the cartridge 104. In this way, the chamber 102 can simply be reloaded from the magazine with another cartridge 104, without having to eject or store a spent cartridge 104, clean out the chamber 102, or remove the gun 100 from the shaft. Combustible cases are commonly used in modern artillery, mortar, and tank rounds. The wall thickness of combustible ordnance is typically such that the combustible material itself provides sufficient structural integrity for the round to withstand usual handling wear and tear. As such, these designs, when chambered, require relatively high pressures to fully eliminate combustion residue.
While there is some precedent for using curved barrels 114 to achieve a diverging projectile pattern, this methodology forces peripheral projectiles 110 to undergo a high G-load turn during launch which induces high stresses on the bodies of the peripheral projectiles that could lead to premature structural failure or premature ignition of the explosive charge within the projectile should it exist.
While the design of the gun 100 in FIG. 1 can be sufficient under certain conditions, it would be desirable to provide a design for repeatedly using combustible cartridges to launch projectiles in a diverging pattern without the requirement for high chamber pressures or without subjecting the projectiles themselves to unnecessarily high stresses during launch. Such a design would provide a safer, more efficient system.